Protective device for electrical circuits.



P. MAGGAHAN- PROTECTIVE DEVICE FOR ELECTRICAL CIRCUITS.

' APPLICATION FILED JAN. 10, 1908.

Patented Dec. 6, 1910.

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P. MAGG'A'HAN. :PROTBOTIVBDBVIGE FOR ELECTRICAL CIRCUITS.

APPLICATION FILED JAI I.'10,1908.

Patented Dec. 6, 1910.

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UNITED ;sTA'r s PATENT o noE.

PAUL MAOGAHAN, or w'ILxINsnUae, PENNSYLVANIA, assreNon, Er mEsNE mm. MENTS, 'ro WESTINGHOUSE ELEc'rmc & MANUFACTURING comrANY, or E181 conPonATIoN' OF PENNSYLVANIA.

PITTSBUEG, PENNSYLVANIA, A

- PROTECTIV DEVICE Eon ELECTRICAL cmcurrs.

To'all whom it may concern:

Befit known that 1,.PAULv MACGAHAN, a citizen of he United States, and aresident of Wllkinsburg, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Protective Devicesfor- Electrical Circuits, of which the following is a specification.

My mventlon relates to protective devices for electrical distributing systems, and articularly to such devices were ada te to protect systems, comprising paralle transmission lines, from injuries that might result from overloads or from reversals of the How of energy therein.

The object of my invention is to provide a system of the character indicated in which an injured line will become disconnected from the remainder ofthe system more promptly when it is traversed by energy in the reverse of normal direction than when traversed by an abnormal amount of. energy in the normal direction. 1

In order to insure themaintenance and reliability of the service rendered by electrical systems, it is a employ parallel transmission lines, and it has heretofore been sought to so protect a system of this character that, upon the oc-- to one line it would be currence of an injury come automatically disconnected from the remainder of the system without disturb ing the other line. This result has been accomplis'hed, only imperfectly however, be-

upon the occurrence of a short-circuit or ground upon one line, current will traverse a portion of that line in the reverse of normal direction,

and due to the same cause, traverse the other line circuit-breakers therein to open as promptly as those in the injured line. For instance. let us consider the most common system of protection heretofore in practical use, in which ordinary overload relays are associqted with circuit-breakers in each transmisslon line at the power house, and 1n which means are provided at each sub-station, for opening circuit-breakers ineach line, either upon the occurrence of an overload. or upon reversal of the flow of energy in the line.

One device which has heretofore been provided for installation at the sub-station end Specification of- Letters Patent. Application filed January 10, 1908. Serial N 0. 410,218.

amount of current traversing common expedient to I an abnormal of time.

Patented Dec. 6, 1910 of parallel transmission lines constitutes the subject-matter of an application, Serial No. 259,388, filed May 8, 1905, b Frank. Conrad, and assigned to the Westinghouse Electrio & Manufacturing Company,

of forces respectively proportional to the amount of energy and the square of the the circuit.- If the current traversing a circuit in connectionwith which the said device is employed exceeds a predetermined amount, the torque that is dependent upon the current alone may exceed that which is dependent upon the product of current, voltage and power factor (which may at times be small on accountof the decrease in voltage and power factor) by such an amount as to effect operation of the deviceandca-use the circuitbreaker to open.

If, fOI QIIIY reason, the direction of the drop of otential in the circuit becomes reversed, tie two torques act in the same direction, and, if the total torque exceeds a predetermined amount, the

the said device being actuated bythe algebraic sum device will operate and cause the circu tbreaker to open. While the said device supplied the demand for a relay that shouldoperate w en the amount of current taken from a system becomes so large as to cause a.

very material reduction in the voltage, and

while it may also be so arranged that it will operate to cause opening of' the circuitbreakers when the circuit is traversed by a smaller amount of energy in the reverse of normal direction than in the'normal direction, 'when short-circuits or low resistance grounds occur near a sub-station and cause very low voltage at the sub-station, the de- -\'ice:associated with an uninjured line may operate by reasonof an overload therein substantially simultaneously with the operation of the device associated with the injured line, which operates owing to a reversal of the flow, of energy. only the disabled line, but the uninjured line as'well, may become disconnected from the remainder of the system.

According to the present circuit-breakers are caused to open -more promptly energy in the reverse of normal direction than when an abnormal amount of current persists in a line for apredetermined length To thisend, the. present .svstem Thus, notv invention, the v i when the clrcuit is traversed by provides two switches for vented by Frank Conrad. and the other switch is operated by means of a wattme'ter device.

To ett'ect operation of the circuit-ln'ealters when the current traversing the circuit exceeds a predetermined amount. a' third switch that is connected in shunt to the aforesaid switches is closed by means of a time limit overload device. Thus, by. the present arrangement. if a ground or short circuit occurs upon one of the lines near a substation. the circuit-breakers at the substation, in the disabled line. will be operated because of the reversal of the flow of energy in that line. while the overload in the unin jured line resulting from the injury to the other line willnot cause the circuit-breakers in the uninjured line to open. unless the overload conditions persist for a predetermined lengthoftime.

The accompanying drawings illustrate diagrammatically systems embodying my invention, thatof Figure 1 being a three-phase system and thatof Fig. 2 a two-phase system.

The system of Fig. 1 comprises two parallel transmission lines 123 and 4-5-6 that feed, at a sub-station, a suitable distributing circuit. 78-9 multiple-pole circuit-breakers 10 and 11 being interposed re spectively in the transmission lines at the sub-station. Each transmission line tected by a similar system of relays, and it has heretofore, been deemed necessary to illustrate and describe completely only the system employed in connection with one of the lines. The circuit-breaker 10 is actuated by an electro-magnetic device comprising a magnet winding 12, the circuit of which includes a battery 13 or any other suitable source of current and is controlled by means of a switch 14 havin an operating or controlling magnet win ing 15, the switch be ing provided with a daslrpot 16 or other suitable means for retarding its operation in such a manner that the period of time which must elapse before the switch will be closed will vary substantially inversely as. the amount of current traversing the operati magnet winding 15. The circuit of the magnet winding 15 is governed by means of three pairs of similar switches 17 and 18 that are disposed in parallel circuits, resistances 19 being connected inshunt to the switches 18. One pair of the switches 17 and 18 is provided for each phase ofthe distributing system and, since the circuit arrangements and the devices provided for phase are substantially identical, they is proeach therefore, be opened unless will i 853,218, granted May 14, 1907, to the \Vest- 10 inghouse Electric & Manufacturing Company, as assignee of \Villiam .L'I. Bradshaw. except that the windin are so arranged that the princi les set orth in the above mentioned app may be utilized. The said instrument comprises a tw9-part magnetizablecore, the core part 21 thereof being provided with a windmg 22 the energizing current for which is proportional in amount to that line conductor 1 and is supplied by a series transformer 23. The core part 21 is also provided with a winding 24 that is connected in closed circuit with a winding upon core part26 of the instrument, a voltage bemg impressed upon the winding 25. which is proportional to that ofone phase of the transmission line 1-2-3, bymeans of a shunt transformer 27.

The device 20 is actuated, as before explained. by the algebraic sum of two torques. respectively proportional to the square of the current traversing the circuit and to the product of the current. voltage and power factor of the circuit, so that the switch 17 will be closed against the action of a spring 28. either when the amount of energy traversing the transmission line 12-3 exceeds a predetermined value, or when ener y traverscs the said line in the reverseot normal direction. The switch 18 is operated by means of a wattmeter device 29 constructed like that set. forth in Patent No. 853.218. current being supplied to winding 30 thereof.

which is proportional in amount to that which traverses line conductor 1. by means of a series transformer 23. and to winding 31 thereof. which is proportional in amount to the voltage of one phase of the transmission line l-2-3, t'ormer 27.

The instrument '29 serves switch 18 open when mission line 1--23 tion, and to close the ergy traverses the transmission line 1--2--3 in the reverse direction. Thus. it is seen that when an ZlbIlOl'll'lill amount of current traverses the ,Ircuit 1-2-- 1-l only switch 1? is closed. the magnet winding 15 to include the resistance 19, which so limits the amount of current that may traverse the winding 15 that the said winding will be energized onlv :feebly and the switch slowly, both for this reason and also on account of the retarding action of. the dashpot 16. The circuit-breaker 10 will not.

and until the abto maintain the energy traverses trans- 111 the normal threenormal amount of current ication of Frank Conrad 75 tra versing 80 by means of the shunt transllt) said switch when en 115 A circuit is then established for 14. will be closed 1-25 has persisted in 20 of Fig. 1.

the circuit 1-2-3 a of time. However, w en current traverses ma be exerted b the'instruments the line 1-2-3 in the reverse of normal dii y y the occurrence 0 short-circuit or ground upon the transmission line.

51 upon rection, the switches 17 and 18 are both closed, and a circuit is established for the winding 15, which does not include the resistance 19. The magnet winding 15 bein l therefore, st-rongl v energized, it prompti y closes the switch 14, and the circuit-breaker i 10 is, accordingly, immediately opened. l Thus, upon occurrence of a short circu t or a low resistance ground upon the transmission line 1-2-3 near the sub-station as, for instance, at 33, ener will be supplied to the sub-station throng the transmission line 4-5-6 and will traverse the line 1-2-3 toward the short-circuit at 33, the amount of energy, of course, being large on account of the short-circuit. The switches 17 and 18 will be closed immediately, on account of the reversal of the flow of energy in the line 1-2-3, and the circuit-breaker 10 will therefore be opened romptly, the disabled line being thereby isconnected from the sub-station. It Wlll be'understood that the I said line will also be disconnected from the remainder of the system at the main station,

modifications other than those which have been illustrated and described may be made in the system without altering its mod operation or epa-rting from the spirit of theiinvention and I desire that all such modifications shall be included within its scope.

1 claim as my invention:

1. The combination with an electrical circuit, circuit-breakers therein, and actuating means for the circuit-breakers, of a switch for controlling the said actuating means, two other switches for controlling the aforesaid switclua resistance in shunt to one-of said other switches, means for closing the unshunted switch when the circuit is traversed by energy rection and by more than a predetermined amount of current, and means for holding the shunted switch open when the circuit is traversed by energy in the normal direction.

in the usual manner by means of ordinary The combination with an electrical ciroverload devices. Since the transmission cuit, circuit -breakers therein, actuating line 4-5-6 is traversed by an abnormal means for the circuit-breakers, and a switch amount of current the switch 1? not shown) associated therewith may be closed. and the switch 14 associated therewith will begin to close, though it cannot close by'the time the circuit-breaker 10 has been opened and the overload conditions upon the line 4-5-6 have. been thereby relieved. In the system of Fig. 2, theinvention is shown as employed i for controlling the said actuating means, two other switches for controlling the afor said switch. and a resistance shunting one of the switches. of means for closing the unshunted switch when the circuit is traversed by energy in the reverse f normal direction and by more than a predetermined amount of current, and means for maintaining the shunted switch open when the cir- \cuit is traversed by energy in the normal in connection with a two-phase system comprising parallel transmission lines 35-36-37-458 and 39-40- 41-42, the circuit offa controlling magnet winding 43 for a circuit-breaker 44 in the transmission line 35-36-37-238, being governed by two time 'limit relay switches 45 and 46, one for each phase of the system. The circuits of magnet windings l7 and 48 of-tlie switches 45 and 46, respectively, are governed by similar airs of switches 49 and 50, t-he'sw1tclr50'be1n actuated by means of a wattmeter 51, an the switch 49 being i traversed by energy in the reverse of'normal actuated by means of an ammetcr device 52 directioi' and for establishing a high-resistthat operates in accordance with'principles. ance circuit therefor when. the circuit is set forth in Patent No.- 794,395 and being traversed by an abnormal amount of ourconstructed substantially like the instrument i rent.

The system (litters further In testimony from that of Fig. 1 in that the springs 5; l are rovided for normally exerting forces 1907. tending to close switches 50 in order to make sure. that the said switches will be closed upon a reversal of the direction of the i flow of energy in the system and to avoid re 1 direction and for closing it when the circuit is traversed by energy in the reverse o't norinal direction.

cuit, a circuit-breaker. therein, means for the circuit-breaker, and a switch for controlling the said actuating means and having a magnet winding, of means for establishing a low-resistance circuit for the whereof, I have hereunto PAUL MAcGAl-IAN.

\Vitnesses:

M. C. Rrirmsrna,

' Bursar HI'NES.

redetermined length lying upon comparatively small torques that a low voltage caused by a It will be readily understood that many e of' 3'. The combination with an electrical eirand actuating said magnet winding when the circuit is subscribed my name this 28rd day of Dec.. 

